Introduction

This page documents the data analysis process used to assess selenium in bird egg tissue for bird eggs collected in the Gilbert Bay assessment unit. The applicable criterion for Se in bird eggs for Gilbert Bay is a nesting season geomean of 12.5 mg/kg dry weight (UAC R317-2-14, table 2.14.2). All data used in this assessment are reported as dry weight.

Read data

sites=as.data.frame(readxl::read_excel('GSL-egg-Se-DWQ.xls', 'Monitoring Locations'))
names(sites)=gsub(" ", "", names(sites))
names(sites)[names(sites)=='MonitoringLocationID']='MonitoringLocationIdentifier'
results=as.data.frame(readxl::read_excel('GSL-egg-Se-DWQ.xls', 'Results'))
names(results)=gsub(" ", "", names(results))
names(results)[names(results)=='MonitoringLocationID']='MonitoringLocationIdentifier'

Site map

wqTools::buildMap(sites=sites) %>% showGroup('Assessment units') %>% leaflet::fitBounds(min(sites$LongitudeMeasure)*0.999, min(sites$LatitudeMeasure)*0.999, max(sites$LongitudeMeasure)*1.001, max(sites$LatitudeMeasure)*1.001)

Figure 1. Egg collection monitoring locations.

Assign AUs

sites=wqTools::assignAUs(sites)

Note - only three sites are witihn the Gilbert Bay AU and used for this assessment.

Subset to Gilbert Bay sites

dim(results)
## [1] 81 73
results=merge(results, sites)
dim(results)
## [1] 81 89
results=subset(results, ASSESS_ID=='UT-L-16020310-001_00')

Calculate geomeans by nesting season (year)

gm_mean=function(x){
    return(exp(mean(log(x))))
}
results$year=lubridate::year(results$ActivityStartDate)
ann_gm=reshape2::dcast(results, year~MonitoringLocationIdentifier, value.var='ResultValue', fun.aggregate=gm_mean)
ann_gm=round(ann_gm, 2)
knitr::kable(ann_gm, caption='Table 1. Bird egg Se concentration geomeans by location and year.')
Table 1. Bird egg Se concentration geomeans by location and year.
year ANTI OGBA SALT
2011 1.55 NaN NaN
2012 1.46 1.43 NaN
2013 0.40 0.49 NaN
2014 0.91 1.04 NaN
2015 1.88 NaN NaN
2016 2.34 2.32 NaN
2017 1.68 NaN 3.69

Boxplot

library(plotly)
plot_ly(data=results, type='box') %>%
    add_trace(x=~year, y=~ResultValue, name=~MonitoringLocationIdentifier) %>% 
        layout(
            boxmode = "group",
            xaxis = list(title = "Year"),
            yaxis = list(side = 'left', title = 'Egg [Se] (mg/kg dry weight)')
        ) %>% 
        config(displaylogo = FALSE,
            modeBarButtonsToRemove = c(
                'sendDataToCloud',
                'hoverClosestCartesian',
                'hoverCompareCartesian',
                'lasso2d',
                'select2d'
            )
        )

Figure 2. Boxplot of egg selenium concentrations among sites and years in the Gilbert Bay assessment unit.

Assessment narrative

Because all nesting season geomeans are less than the applicable numeric criterion of 12.5 mg/kg dry weight, Gilbert Bay is fully supporting for the class 5A bird egg selenium criterion. In addition, all seasonal geomeans were lower than the lowest egg Se concentration trigger identified in R317-2-14 (5.0 mg/kg). DWQ will continue routine monitoring of egg tissue in GSL.

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